The method explained here uses MoreFunctionsForAddressBook.

thx for your prompt reply sfhowes apparently v. 60 is not compatible with this add on i found a solution which is to use cmd.exe to copy all separate .vcf files into one file navigate to the .vcf folder and enter: >copy *.vcf to merged.vcf this file can be imported with all contacts

I'm glad you found an effective way to merge vCards, but for the sake of others who may read this, note that MoreFunctionsForAddressBook is in fact compatible with TB 60, as can be seen from the change log at the bottom of the page:

Changelog 1.0b8 version - compatibility with Thuderbird 60.

thx for clarifying that - i must have read an old post before it upgraded to work with tbird v. 60.8

Hello, I have the same problem. After today's fresh installation of Thunderbird 68.2.2 (64-Bit) only the "Import/Export-Tools NG V 4.04 from 24.11.2019" (Add-on from TB-Add-ons Site) is described to be compatible with TB V 68.2.2, not any more the above mentioned "MoreFunctionsForAddressbook" . But the actually installed "Import/Export-Tools NG V 4.04 by 24.11.2019" has still the exact problem not to support "Cntrl + A" or other "options" (using shift + mark first and last) known from normal Windows-Explorer to select alle entries/.vcf-files of a folder.

Did I understand something wrong or can you provide a working solution?

Thanks in advance.

ImportExport-Tools NG works only for mail, not contacts. The only method I'm aware of for importing multiple vCards in TB 68 is with the CardBook add-on. You can also try the merging operation mentioned above, or use the MoreFunctionsForAddressbook add-on on a computer with TB 60.